In the practice of orthodontia it is often necessary to move into a more favorable position at least one tooth with respect to the other teeth. This is accomplished typically through the use of what is referred to as Class II-Type Devices which usually comprise the provision of an elastic member or coil spring between one point on a tooth or archwire on one of the jaws to a tooth or point on the archwire on the other jaw. Examples of orthodontic tensioning devices of the prior art are illustrated in U.S. Pat. Nos. 3,618,214; 3,654,702; 936,938; 3,921,295; 4,199,865; 4,315,739; 4,382,783; 4,462,800; 4,849,032; and 4,330,271. As can be seen from the foregoing patents, prior art tensioning devices come in a variety of forms.
While prior art elastic tensioning devices such as rubberbands and the like provide a wide degree of motion, a significant problem with such devices is that reliance is often placed on patient cooperation as these devices are required to be changed quite frequently. An additional disadvantage of elastic-type devices is that after a short time, these devices exhibit stress relaxation which results in substantially less force than that needed to maintain the elastomer in its stretched position, thus reducing the amount of force being applied. A still further problem with such devices is that they take a permanent set reducing its effectiveness at lower elongations.
Steel coil springs and other mechanical-type devices which exist in the prior art have the disadvantage in that the amount a patient may open his mouth is limited, or becomes extremely uncomfortable the wider the patient opens his mouth. Furthermore, with typical prior art steel coil springs, the force applied varies widely in response to large deflections which result in a wide variation of forces being applied to the tooth as the patient opens and closes his or her mouth. Another problem with prior art-type devices is that occasionally a patient may open his mouth to such an extent that the tensioning device will go beyond its elastic limit. The tensioning device is so stretched and a permanent set takes place, thus reducing the effectiveness of the device, especially when the patient has his mouth closed or barely open. Further, open coil springs present the possibility of trapping food therein.
Applicants have invented an improved orthodontic tensioning device which minimizes or avoids the problems the prior art. The orthodontic tensioning device of the present invention provides a relatively constant force to the malocclused teeth or jaws, is capable of high elongation and maintaining a substantial portion of the initial force applied. Further, the device is simple to assemble, of relatively low cost to manufacture, easy to use, and provides means for easily adjusting the force to be applied.